1. Field of the Invention
The present invention relates to a cylinder head for a DOHC internal combustion engine of the kind having four valves per cylinder.
2. Description of the Prior Art
It is a known DOHC internal combustion engine that has two intake valves and two exhaust valves per cylinder. The intake valves and the exhaust valves are driven by two independent camshafts installed on a cylinder head.
An internal combustion engine is constructed so as to draw lubricating oil from an oil pan and supply it to a valve drive train, etc. for lubrication of same.
The internal combustion engine of the above described kind has a difficulty in forming an oil passage in the cylinder head due to the complicated structure of the valve drive train and the cylinder head. For example, in a certain case an oil supply passage can be formed in the cylinder head in such a way as to penetrate therethrough but an oil return passage cannot in the similar manner.
For this reason, no oil return passage has heretofore been formed in the cylinder head for the engine of the above described kind so that the oil having lubricated the valve drive train, etc. flows from an upper deck of the cylinder head down to a camshaft drive chain chamber from which it drops into the oil pan. However, since the upper the deck is far apart from the camshaft drive chain chamber, there is a difficulty of rapidly and assuredly returning lubricating oil to the oil pan and therefore there is a possibility of stagnation of lubricating oil and therefore a lack of same.
Further, some internal combustion engines of the above described kind are constructed so that movement of cams of a camshaft is transmitted to intake and exhaust valves by way of rocker arms of the end pivot type, i.e., of the type adapted to pivot at one end. When this is the case, each valve is driven by an independent rocker arm, resulting in an increased number of constituent parts as lash adjusters, etc. and an increased number of portions to be lubricated. Accordingly, a further complicated structre of a cylinder head results as disclosed in Japanese provisional patent publication No. 60-79141.